The ripple voltage drops to 5 mV peak-to-peak when measured at the board edge. The reduction of the ripple voltage from 8 mV peak-to-peak when measured across the local output capacitor to 5 mV peak-to-peak at the board edge is due to the board's parasitics, which act as an additional output filter. This location is analogous to a decoupling capacitor at the load further away from the buck regulator.